FIGS. 1, 2A, 2B, and 3 depict the color filtration of a conventional digital camera.
FIG. 1 shows the internal structure of a chromatic sensing unit adopting a color filter (3) in a digital camera, and changes in the incident light after passing through the color filter (3). Referring to FIG. 1, light (1) incident from the outside is converged by a microlens (2), and the light (4) passing through the color filter (3) corresponding to each pixel enters the photodiode (6). The reference numeral 5 denotes a silicon oxide layer. The chromatic sensing unit used in a digital camera is configured so that a color filter mosaic, which is a grid of the primary color filters (red-green-blue, “RGB”) or complementary color filters (yellow/cyan/green/magenta, “Ye/Cy/G/Mg”), is applied on a photodiode (6) located in each pixel. This allows only light (4) of a color corresponding to the color filter (3) for each pixel to be transmitted so that the corresponding photodiode (6) reacts with the light (4).
FIGS. 2A and 2B show color filter mosaic arrays of pixel sensors adopting the RGB primary and Ye/Cy/G/Mg complementary color filters in a conventional digital camera, respectively. The color filter mosaic arrays of FIGS. 2A and 2B correspond to the color filter (3) of FIG. 1.
Automatic focusing (AF) of a digital camera is a technique of focusing on an object by analyzing the high frequency content of an image of the object input from an image sensing unit while moving a focusing lens. This focusing technique is allowed only when an automatic brightness level is greater than the minimum brightness. The brightness level of the light (4) that passes through the color filter (3) physically decreases compared with incident light (1) prior to passing through the color filter (3). Thus, since the brightness level recognized by the sensor becomes lower after light passes through the color filter (3), the amplitude of the signal output from the sensor decreases. Due to the changes in brightness levels as light passes through the filter (3), the brightness level of the incident light (1) onto the sensor decreases to less than a brightness threshold in a low brightness environment. This may cause the output of the optical sensor to decrease to the extent automatic focusing cannot be performed.